A semiconductor laser comprises a body of material, generally including group III-V compounds or alloys of such compounds, having a thin active region between cladding regions of opposite conductivity type. Double heterostructure lasers, such as those disclosed by Botez in U.S. Pat. No. 4,347,486 and by Connolly et al. in U.S. patent application Ser. No. 367,212 filed Apr. 9, 1982, U.S. Pat. No. 4,461,008, which are incorporated herein by reference, are capable of producing a single transverse (the direction perpendicular to the plane of the layers) and lateral (the direction in the plane of the layers and perpendicular to the direction of light propagation) mode, high power laser beam. These lasers have a guide layer adjacent to the active layer so that light generated in the active layer propagates mostly in the adjacent guide layer, thereby producing a much larger emitting area. However, the emitting area is still small, typically on the order of several square micrometers (.mu.m). The local power density is thus very high and may result in damage to the emitting end face which can be either catastrophic in nature or a slow, long term end face degradation.
To avoid either type of damage the output power density at the end face is held below the threshold at which such damage occurs. A transparent passivation coating, as disclosed by Ladany et al. in U.S. Pat. No. 4,178,564, incorporated herein by reference, may be placed on the emitting end face to increase the threshold at which the damage occurs. This combination of measures reduces the incidence of damage but the laser's inherent output power capability is not fully utilized.
Catastrophic damage may be caused by local heating of the end face to a temperature close to the melting temperature of the material by absorption of the laser light. To eliminate catastrophic damage and degradation, lasers have been fabricated in which the light absorbing active layer does not extend to the end face with a non-absorbing waveguide between the active layer and the end face, as disclosed, for example, by Botez in U.S. patent application Ser. No. 437,838 filed Oct. 29, 1982, U.S. Pat. No. 4,523,316, and incorporated herein by reference. Such devices have shown an increase in the threshold powers at which the long term and catastrophic damage occur of between about five and ten times.
Such devices do not, however, provide strong lateral mode control in the non-absorbing region adjacent to the emitting end face. Thus, the lateral mode character of the output light beam will depend upon the length of the non-absorbing region which will differ from device to device because of the inaccuracy present in the cleaving process used to form the end faces. Thus, it would be desirable to have a semiconductor laser with a non-absorbing end face and having lateral mode control.